A common problem with the reception of digital signals is that in addition to noise the transmission channel also causes linear and non-linear distortions in the signal. Prior art methods for eliminating the effects of linear distortions from the received signal include linear and non-linear transversal equalizers, which may be adaptive so that they adapt to possible changes in the transmission channel during the signal transmission.
To compensate for non-linear distortions, International Application PCT/FI89/00037 discloses an adaptive detection method for quantized signals, which utilizes the self-organizing map principle during detection to automatically take into account the effects of changes taking place in the channel properties on a signal constellation used in the detection. The same method is described in Kohonen, Raivio, Simula, Venta, Henriksson: An Adaptive Discrete-Signal Detector Based on Self-Organizing Maps. International Joint Conference on Neural Networks IJCNN-90-WASH DC, Jan. 15-19, 1990, Washington D.C., Vol. II, P. II-249-52.
The above-described solutions are not, however, able to operate in an optimal way in surroundings where both distortion types occur simultaneously. A linear or non-liner transversal equalizer is not able to compensate for non-linear distortions (or is able only limitedly), and the map method compensating for non-linear distortions is disturbed by the linear distortions.